The Proteome of Biologically Active Membrane Vesicles from Piscirickettsia salmonis LF-89 Type Strain Identifies Plasmid-Encoded Putative Toxins

Abstract

<i>Piscirickettsia salmonis</i> is the predominant bacterial pathogen affecting the Chilean salmonid industry. This bacterium is the etiological agent of piscirickettsiosis, a significant fish disease. Membrane vesicles (MVs) released by <i>P. salmonis</i> deliver several virulence factors to host cells. To improve on existing knowledge for the pathogenicity-associated functions of <i>P. salmonis</i> MVs, we studied the proteome of purified MVs from the <i>P. salmonis</i> LF-89 type strain using multidimensional protein identification technology. Initially, the cytotoxicity of different MV concentration purified from <i>P. salmonis</i> LF-89 was confirmed in an <i>in vivo</i> adult zebrafish infection model. The cumulative mortality of zebrafish injected with MVs showed a dose-dependent pattern. Analyses identified 452 proteins of different subcellular origins; most of them were associated with the cytoplasmic compartment and were mainly related to key functions for pathogen survival. Interestingly, previously unidentified putative virulence-related proteins were identified in <i>P. salmonis</i> MVs, such as outer membrane porin F and hemolysin. Additionally, five amino acid sequences corresponding to the <i>Bordetella pertussis</i> toxin subunit 1 and two amino acid sequences corresponding to the heat-labile enterotoxin alpha chain of <i>Escherichia coli</i> were located in the <i>P. salmonis</i> MV proteome. Curiously, these putative toxins were located in a plasmid region of <i>P. salmonis</i> LF-89. Based on the identified proteins, we propose that the protein composition of <i>P. salmonis</i> LF-89 MVs could reflect total protein characteristics of this <i>P. salmonis</i> type strain.